Measurement reporting in a telecommunication system

ABSTRACT

The basic idea of the present invention is to specify at least two different triggers for sending a measurement report from the mobile station to the network. According to the invention, the network specifies the triggers to be used in different measurement report types. The triggers are preferably upper or lower threshold values for parameters of the radio signal. In response to having detected that the measured value has exceeded its upper threshold value or gone under its lower threshold, the mobile station sends the network a measurement report.

FIELD OF THE INVENTION

This invention concerns reporting of measurements on radio interface ina telecommunication system.

BACKGROUND OF THE INVENTION

In mobile telecommunication systems mobile stations MS can use theservices provided by the network using radio connections. The radioconnection uses the channels of called radio interface between themobile station and a base station of the mobile telecommunicationnetwork. Only a limited bandwidth on the radio spectrum is allocated tobe used by the telecommunication systems. To gain capacity enough, thechannels must be used again as densely as possible. To achieve this, thecoverage area of the system is divided into cells, each being served byone base station. Due to this, the mobile telecommunication systems areoften also called cellular systems.

The network elements and the internal relation between the networkelements of a mobile telecommunication system are presented in FIG. 1.The network presented in the figure is in accordance with the UMTSsystem currently being standardized by ETSI (European TelecommunicationsStandards Institute). The network comprises base stations BTS (BaseTransceiver Station), that can establish connections with the mobilestations MS, Radio Network Controllers RNC controlling the usage of basestations and Mobile Switching Centers MSC controlling the RNC's. Inaddition, the network comprises a Network Management System NMS, withthe help of which the operator can modify the parameters of the othernetwork elements. The interface between the MSG and the RNC's isgenerally called the lu interface. The interface between the RNC's andthe BTS's is the lubis interface and the interface between the BTS andthe MS's the radio interface. According to some proposals, an interfacelur between the RNC's is specified.

The calls of a mobile station are routed from the BTS via the RNC to theMSC. MSC switches the calls to other mobile switching centers or to thefixed network. The calls can as well be routed to another mobile stationunder the same MSC, or possibly even under the same BTS.

The radio interface between the base stations and the mobile stationsmay be divided into channels using a plurality of divisions. Knownmethods of division are, for example, Time Division Multiplexing TDM,Frequency Division Multiplexing FDM and Code Division Multiplex CDM. InTDM systems, the spectrum allocated for the system is divided intosuccessive time frames consisting of time slots, each time slot definingone channel. In FDM the channel is defined by the frequency used in theconnection. In CDM the channel is defined by the spreading code used inthe connection. These methods can be used separately or be combined.

To be able to successfully communicate with the mobiletelecommunications network, the mobile station continuously monitors theradio signals sent by the base stations. In the idle mode the mobilesdecode the strongest signal received, and when needed request theestablishment of a connection from the base station transmitting thissignal.

During an active connection, the connection can be moved from one basestation to another. The connection can be moved from one base station toanother by simply rerouting the signal, which is called hard handover.The system interference can be decreased and thus the capacity increasedespecially in CDMA (Code Division Multiple Access) systems utilizing CDMby using soft handovers in which the mobile has simultaneouslyconnections with a plurality of base stations, these base stationsforming the so called active set of the connection.

The handover may be

-   -   intra-cell handovers    -   inter-cell handovers between two base stations under the same        radio network controller    -   inter-RNC handovers between two RNC's under the same MSC, or    -   inter MSC handover between two cells under different MSC's.

In addition, the handover can be divided into intra-frequency handoversin which all the channels involved in the handover procedure are on thesame frequency and inter-frequency handovers, in which there arechannels from at least two frequencies involved in the handoverprocedure.

To be able to establish the handovers to right base stations during anactive connection, the mobile station continuously measures the radiosignals from the base stations it is in connection with as well as theirneighboring base stations. The measurement results are transmitted tothe network using the measurement reporting scheme specified in thesystem. Based on the reports, the network initiates the handover whenthe mobile station would have a better or at least sufficiently goodradio connection to another base station.

In addition to the network initiated handovers, also mobile evaluatedhandovers are known. In an exemplary description of a mobile evaluatedhandover, the mobile station monitors the signal levels received fromneighboring base stations and reports to the network those beaconsignals which are above or below a given set of thresholds. Thosethresholds can be dynamically adjusted as will be explained in thefollowing. Based oh this reporting scheme, the network will decidewhether the active set of the connection is to be changed.

Two type of thresholds are used: the first one to report beacons withsufficient power to be used for coherent demodulation, and the secondone to report beacons whose power has declined to a level where it isnot beneficial to be used for receiving the sent information. Based onthis information, the network orders the MS to add or remove basestation signals from its active set.

While soft handover improves overall performance it may in somesituations negatively impact system capacity and network resources. Thisis due to the unnecessary branches between the MS and the base stationsin the active set. On the downlink direction from the base stations tothe mobile station, excessive branch reduces system capacity while onthe uplink direction from the mobile station to the base stations, itcosts more network resources.

To solve this problem, the principle of dynamic thresholds for activeset management is known in prior art. In this method, the MS detectsbeacons crossing a given static threshold T1. When crossing thisthreshold the beacon is moved to a candidate set. It is then searchedmore frequently and tested against a second dynamic threshold T2. Thissecond threshold T2 will test if the beacon is worth adding to theactive set.

When the beacons corresponding to the branches in the active set areweak, adding an additional branch signal, even a poor one, will improveperformance. In these situations, a relatively low value of T2 is used.When there is one or more dominant beacons, adding an additional weakerbranch whose beacon signal is above T1 will not improve performance butwill utilize more network resources. In these situations a higher valueof T2 is used.

After detecting a base station signal above T2, the MS will report itback to the network. The network will then set up the handover resourcesand order the MS to coherently demodulate the signal of this additionalbranch.

Beacons can be dropped from the active set according to the sameprinciples. When the beacon strength decreases below a dynamic thresholdT3, the handover connection is removed, and the beacon is moved back tothe candidate set. The threshold T3 is a function of the total energy ofbeacons in the active set. When beacons in the active set are weak,removal a branch, even a weak one, will decrease performance. In thesesituations, a relatively low value of T3 is used. When there is one ormore dominant branches, removal of a weaker signal will not decreaseperformance but will make the utilization of the network resources moreefficient. In these situations a higher value of T3 is used. Branchesnot contributing sufficiently to the total received energy will bedropped. When further decreasing below a static threshold T4 a beacon isremoved from the candidate set.

To be able to control the connection, the network needs in differentsituations different kinds and different amount of measurementinformation. The more information is sent the more efficient thehandover algorithm are. However, the more information the mobile stationsends the network, the more radio resources are spent. Thus, themeasurement reporting schemes according to prior art are alwayscompromises between the efficiency of the handover algorithms and theusage of radio resources.

As the usage of mobile telecommunication systems and multimediaapplications requiring large bandwidths is growing the present methodsare no longer sufficient, thus limiting the performance of the mobiletelecommunication networks. The objective of the present invention is aflexible measurement reporting scheme which solves this problem.

SUMMARY OF THE INVENTION

The basic idea of the present invention is to specify at least twodifferent triggers for sending a measurement report from the mobilestation to the network. According to the invention, the networkspecifies the triggers to be used for different measurement reporttypes. The triggers are preferably upper or lower threshold values forparameters of the radio signal, timer conditions, etc. In response tohaving detected that the measured value has exceeded its upper thresholdvalue or gone under its lower threshold, the mobile station sends thenetwork a measurement report.

According to a preferred embodiment, one or a plurality of the triggerscan be inactivated by the network. However, at least one trigger mustalways be active.

According to one preferred embodiment, the triggers, i.e. the thresholdvalues are defined separately for downlink and uplink directions. Inaddition, it is specified how the outputs of these triggers are to becombined. For example, it may be determined whether the measurementreport is to be sent when both the uplink and downlink conditions aremet, when either of them is met, based entirely on the downlinkcondition or based entirely on the uplink condition.

In one preferred embodiment, one of the measurement report types ismobile evaluated handover measurement report. Such a report is triggeredin the mobile station when at least one upper threshold for the radiosignal parameter for a mobile evaluated handover is exceeded or lowerthreshold gone under.

According to another preferred embodiment, one of the measurement reporttypes is periodic handover measurement report. Such a report istriggered periodically with a period set by the network.

According to yet another embodiment, one of the measurement report typesis a condition change based measurement report. In this report type, thetransmission of the measurement report is triggered by a change in theradio signal parameter exceeding a threshold given by the network.

BRIEF DESCRIPTION OF THE FIGURES

The invention is described more closely with reference to theaccompanying schematic drawings, in which

FIG. 1 shows a mobile telecommunication system;

FIG. 2 shows a measurement reporting scheme;

FIG. 3 shows the structure of a MEHO algorithm;

FIGS. 4, 5, 6,7 and 8 each show a decision flow chart;

FIG. 9 shows functional entities in a telecommunication network, and

FIG. 10 shows functional entities in a mobile station.

DETAILED DESCRIPTION OF THE INVENTION

The basic idea of the invention is presented schematically in FIG. 2. Instage G00, a plurality of triggers is defined in the network. In theexemplary embodiment presented in the figure, three triggers, TRIGGER 1,TRIGGER 2 and TRIGGER 3 are defined. However, is must be noted here thatthe invention is not limited to the use of exactly three triggers, butthe number of triggers may be any number equal to or larger than two.The mobile station is informed about these triggers.

The mobile station continuously measures the radio signals from the basestations in the neighborhood (stage G01). In these measurements, themobile acquires information necessary to compare the measurement resultsto the triggers.

At stage G02 the measurement results are compared to TRIGGER 1. If theconditions launching the trigger are met (decision stage G03), ameasurement report of type 1 is sent to the network at stage G10, andthe procedure continues to stage G01. If the conditions are not met, theprocedure continues to stage G04.

At stage G04 the measurement results are compared to TRIGGER 2. If theconditions launching the trigger are met (decision stage G04), ameasurement report of type 2 is sent to the network at stage G20, andthe procedure continues to stage G01. If the conditions are not met, theprocedure continues to stage G06.

At stage G06 the measurement results are compared to TRIGGER 3. If theconditions launching the trigger are met (decision stage G07), ameasurement report of type 3 is sent to the network at stage G30. Theprocedure then continues to stage G01.

According to a preferred embodiment, one or a plurality of the triggerscan be inactivated by the network. Thus, the network is capable offlexibly adjusting the reporting scheme. For example, when in the innerparts of a cell, the mobile station has a very good link with the basestation. In such a situation, it is adequate that the mobile stationinforms the network, when the link gets worse than a given threshold. Inthis situation, only one of the trigger conditions is active. When themobile station reaches the border region of the cell, this thresholdcondition is met, and the mobile station sends the network a measurementreport. Upon receiving this report, the network decides, that the mobilestation should be followed more closely, and orders the mobile stationto start sending the measurement reports periodically and at once whenthe links monitor meet a second threshold condition. Now, two triggerconditions are active. In all situations, however, at least one triggercondition must be active.

In FIG. 2, the comparisons at stages G02, G04 and G06 are shown to beserial. However, they may as well be implemented as parallel processes.

In the following, three preferred types of measurement reports arespecified more closely. The types are particularly preferred when usinga Wideband CDMA (WCDMA) system utilising soft handovers. The reporttypes are Mobile Evaluated HandOver (MEHO), periodic measurementreporting and condition change based measurement reporting.

The Mobile Evaluated Handover

In this context mobile evaluated handover means, that a handovermeasurement algorithm situated in the mobile triggers the handoverreport. The actual HO decision is always performed by the network. Thehandover report types can be further divided into intra-frequency andinter-frequency handover report types.

The Intra-Frequency Handover

The algorithm presented in the following includes the possibility to useinformation about the downlink (DL), uplink (UL) or both as the triggerfor the HO report. Also this scheme provides a flexible means to controlthe information content of the HO report. The actual thresholds andtimers in the algorithm are selected to be such, that a wide variety ofHO algorithms can be constructed by the appropriate setting of these

The mobile station continuously performs measurements on the radiosignals from different BTS's according to the procedure described in thefollowing.

The mobile measures the received power of the beacon channel for BTSi.This power is denoted as Prx,i (mW). The MS performs this measurementfor time period t (a parameter preferably set by the network). The valueof P_(rx,i) is averaged over the measurement period. The result of thisoperation is denoted as P_ave_(rx,i). When the measurement is completed,the path loss estimate, denoted as Li (dB), is calculated as:$\begin{matrix}{L_{i} = {{- 10}\quad{\log_{10}\left( \frac{{P\_ ave}_{{rx},i}}{{P\_ beacon}_{\quad_{{tx},i}}} \right)}}} & (1)\end{matrix}$

In (1), the unit of P_beacont_(tx,i) is mW.

During the same measurement period t the MS also estimates theinterference power of the beacon channel before or after (this ispreferably a parameter defined by the network) correlating the receivedsum signal with the spreading code. The values calculated before orafter the correlation differ due to the fact that the correlationremarkably reduces the interference caused by other connections. Thisinterference is denoted as I_(i) (mW). The interference is also averagedover the measurement period. After the averaging has been performed, theaverage value is converted into dBm. This average is denoted asI_ave_(i).

The MS is also to receive, e.g. on the beacon channel the DL_offsetvalue of BTS_(i), denoted as DL_offset_(i) (dB), which is a relativelystable parameter and there is thus no need to re-receive it for eachmeasurement period. The purpose of this base station specific parameteris to specify fro different cell sizes. The mobiles are handed over froma first set of cells more willingly than from a second set of cells.These cells of the first set thus become smaller than the cells of theother set. The offset value can be seen as an additional base stationspecific part of the threshold values that are soon to be presented moreclosely.

From the above information the MS is to calculate one DL HO measurementS_(dl,i) sample asS _(dl,i) =L _(i) +I _(ave,i) +DL_offset_(i)  (2)

S_(dl,i) is thus a measure for the carrier to interference ratio CIR ofthe measured signal. It is to be noted that the larger the value ofS_(dl,i), the worse the link from the base station to the mobile stationis. The scope of this invention is not limited to the use of thisparticular measure, but other measures of the link quality may as wellbe used when implementing the present invention. As one example, the biterror ratio BER in the received radio signal can be used as the measure.

The MS is also to receive, e.g. on the beacon channel, the totalinterference power, I_(ul,i) (dBm) at the BTS_(i) and the UL offsetvalue, UL_offset_(i) (dB) of BTS_(i). The MS is then to calculate thevalue of one UL HO measurement sample asS _(ul,i) =L _(i) +I _(ul,i) +UL_offset_(i)  (3)

When these measurements and calculations have been performed for BTS_(i)the MS is then to place the results as the first elements in the vectorsL_vect_(i) (for the value of L_(i)), S_vect_(dl,i) (for the value ofS_(dl,i)) and S_vect_(ul,i) (for the value of S_(ul,i)). The lastelement of these vectors is discarded. The vectors comprise the historyof the measurement results. The length of the history maintained,defined by the length n of these vectors is a network parameter.

Having performed the measurements for this base station signal the MSchecks whether a MEHO report is to be transmitted according to the HOalgorithm described in the following chapter. The argument of thealgorithm may be for instance either median or mean of the vectorsS_vect_(dl,i) and S_vect_(ul,i), and is preferable defined by thenetwork. In addition, the MS starts to measure the beacon signaltransmitted by the next BTS BTS_(i+1).

The HO algorithm is used to trigger the transmission of the MEHOmeasurement report. In the algorithm the UL and DL directions oftransmission are treated separately. So actually two algorithms canfunction in the MS independently. The network can command the MS to useeither one of them or both for the triggering of measurement reporttransmission. It should be noted, however, that the active set is alwaysthe same for both directions of transfer.

The algorithm includes the below thresholds:

-   -   1. Branch addition threshold denoted in this document as        BA_abs_(th) and BA_rel_(th),    -   2. Branch deletion threshold denoted in this document as        BD_abs_(th) and BD_rel_(th), and    -   3. Branch replacement threshold denoted in this document as        BR_rel_(th)

For the thresholds 1 and 2, both an absolute and a relative thresholdare defined. Separate values can be defined for the uplink and thedownlink directions. The thresholds are used in Branch Addition (BA),the Branch Deletion (BD) and the Branch Replacement (BR) decision units.These units may be implemented as hardware units, software blocks or acombination of these.

The basic structure of these algorithms is presented in FIG. 3. Theuplink comparison unit ULU compares the measurement results of theuplink radio signals to triggers defined by the thresholds set to thesesignals, and outputs a logical truth value. The downlink comparison unitDLU compares the measurement results of the downlink radio signals totriggers defined by the thresholds set to these signals, and outputs alogical truth value. The results of ULU and DLU are combined to onelogical signal using a logical function. The logical value may be, forexample, AND or OR function, or a function outputting directly one ofthe input values of the block. The truth value of this signal isverified, and a report is sent if the truth value is TRUE, for example.Of course, using a different logical function when combining the outputsof ULU and DLU, it can be defined that the report is sent if the truthvalue is FALSE.

The parallel decision units BA, BD and BR shown in FIG. 3 are used indifferent situations. BA is used when the base station is not in theactive set of the connection, and the number of links between the MS andBTS's in the active set is less than a given limit N_(AS,max). The valueof N_(AS,max) is a preferably a parameter set by the network.

BD is used when the base station is in the active set of the connection.To prevent ping-pong effect, the logical functions of the BA and BDblocks must be consistent so that the same measurement values for a linkbetween the MS and a BTS may not cause both the units to trigger ameasurement report suggesting an addition or deletion of the same link.For example, if logical functions AND and OR are used, the value OR maynot be used in both the decision blocks.

BR is used when the base station is not in the active set of theconnection and the number of links between the MS and BTS's in theactive set is equal to the limit N_(AS,max). This decision unit is usedto replace on link of the active set by another one having better radiocharacteristics.

One algorithmic implementation of the downlink comparison unit DLU ofthe branch addition algorithm BA is shown in FIG. 4. The algorithm isused for beacon signals from base stations that do not belong to theactive set. At stage A1 it is checked whether the number of basestations in the active set is less than a predefined limit, i.e. whetherthe active set is full. As an example, the limit 3 can be used here. Ifthe active set is full, the branch replacement algorithm is selectedinstead of this algorithm (stage A10).

If the active set is not full the procedure proceeds to stage A2, A3 andA4, in which

-   -   it is checked whether new measurement results have been received        (stage A2),    -   S_(i,DL) is compared to absolute threshold BA_abs_(th,DL), and    -   S_(i,DL) is compared to threshold S_best_(i,DL)+BA_rel_(th,DL),        in which S_best_(i,DL) id the value measured for the best active        branch.

If new results have been received and both the threshold valuesBA_abs_(th,DL) and S_best_(i,DL)+BA_rel_(th,DL) are higher thanS_(i,DL), the output of the DLU is set to TRUE.

The uplink branch can be implemented using a similar algorithm. If newresults for the uplink have been received and both the threshold valuesBA_abs_(th,UL) and S_best_(i,UL)−BA_rel_(th,UL) are higher thanS_(i,UL), the output of the ULU is set to TRUE. The threshold valuesBA_abs_(th,DL)/BA_abs_(th,UL) and BA_rel_(th,DL)/BA_rel_(th,UL) used indifferent directions may be different from each other or identical.

The values of the DLU and ULU algorithms are inputted into the logicalfunction, as shown in FIG. 3. MEHO measurement report is sent if thefunction outputs a value TRUE. For example, if the logical value used isAND, the MEHO measurement report is sent when both the ULU and DLU havevalue TRUE.

An algorithmic implementation of the downlink comparison unit DLU of thebranch deletion algorithm BD is shown in FIG. 5. This algorithm is usedfor beacon signals from base stations that belong to the active set.

It is first checked whether new measurement results have been received(stage D2). The measurement result S_(i,DL) is compared to thresholdsBD_abs_(th,UL) (stage D3) and S_best_(i,DL)+BD_rel_(th,UL) (stage D4).If either of these thresholds is lower than S_(i,DL), the DLU is set toTRUE (stage D5). Otherwise, DLU is set to FALSE (stage D10) and the nextbeacon signal in the active set is measured.

A similar comparison in made between the uplink measurement results anduplink thresholds to define the value of ULU. DLU and ULU are combinedusing a logical function defined by the network to make a decisionwhether to send or not to send a MEHO measurement report. To prevent theping-pong effect, the logical function used is selected so that the samemeasurement results never cause the BA to request the addition of abranch and the BD to delete the same branch. To meet this requirement,only one of the logical functions used in BA and BD algorithms accordingto the same reporting option may be a logical OR function.

An algorithmic implementation of the downlink comparison unit DLU of thebranch replacement algorithm BR is shown in FIG. 6. The algorithm isused for beacon signals from base stations that do not belong to theactive set. At stage R1 it is checked whether the number of basestations in the active set is equal a predefined limit, i.e. whether theactive set is full. As an example, the limit 3 can be used here. If theactive set is not full, the branch addition algorithm is selectedinstead of this algorithm (stage R10).

If the active set is full the procedure proceeds to stage in which it ischecked Whether new measurement results have been received (stage R2).If no new measurement results have been received, the next beacon signalis studied. If new measurement result S_(i,DL) has been received it iscompared at stage R3 to the measurement value S_worst_(i,DL) of theworst link in the active set. If S_worst_(i,DL) exceeds S_(i,DL) with amargin of BR_rel_(th) DLU is set to TRUE (stage R4). Otherwise ULU isset to FALSE (stage R20) and the measurements on a next BTS notbelonging to the active set studied.

The uplink branch can be implemented using a similar algorithm. In thiscomparison, S_(i,UL) is compared to S_worst_(i,DL) of the worst link inthe active set. If S_(i,DL) exceeds S_worst_(i,DL) with a margin ofBR_rel_(th) DLU is set to TRUE. The margin values BR_rel_(th) arepreferably identical in downlink and uplink directions, but alsodifferent values in different directions can be used. This is aparameter that is defined by the network. DLU and ULU are combined usinga logical function to make a decision whether to send or not to send anMEHO measurement report. The logical function is preferably a logicalAND function. In another preferred embodiment, the logical function canbe adjusted freely by the network. The output of the logical functioncan be, e.g. the truth value of DLU or ULU.

When the MEHO algorithms in the mobile station trigger the measurementreport the status of the M best cells/sectors is transmitted. Thetransmitted measurement report is always to include the appropriatevalues for the active set. The M best cells/sectors are determined byusing the values of S_(i,dl) or S_(i,ul) depending on whether it was DLor UL algorithm that triggered the report. The contents of the report ispreferably determined with an message sent from the network. Themeasurement report includes, for example the following values for eachcell/sector to be reported. These values are the filtered values.

-   -   1. S_(i,dl)    -   2. S_(i,ul)    -   3. L_(i)

It should be noted, that the measurement report can include informationonly about neighbour BTSs whose beacon signals have been decoded. Thusthe handover report has to include the information of the number of BTSsthat are being reported.

The information included in the measurement report may preferably bedefined by the network. For example, the number of beacon signals whosepower level is to be reported in a measurement report is preferablydefined by the network.

The Inter-Frequency HO

The inter-frequency measurements are always initiated by the network.Thus the mobile can perform inter-frequency MEHO only after the networkhas first commanded the MS to start the inter-frequency HO measurements.

There are at least three different reasons for inter-frequency HO:

-   -   1. Coverage. The MS is e.g. exiting the coverage area of a        microcell and has to hand over to a macrocell. This case may be        relatively simple. For example if the branch deletion has        triggered a measurement report and only one branch is active the        conclusion by the network is, that the MS is exiting the        coverage area. The network responds to this by transmitting a        message ‘start i-f measurements’. This message includes the        possible candidate BTSs. The mobile would then start searching        for a stronger BTS on the other frequency. The transmission of        the measurement report is triggered when the MS finds a        candidate BTS on the other (new) frequency that is stronger than        the best active branch on the current frequency.    -   2. Load. If for some reason the load on the used frequency is        higher than on some other available frequency an inter-frequency        HO may be appropriate. This situation would probably be known        only by the network. After the network has detected the overload        situation the actions are the same as in case 1    -   3. Mobile speed. The speed of the MS is so high, that an        excessive amount of handovers are needed if the MS is connected        to the microcell layer. This is an item for further study. The        most crucial question is the detection of the MS speed. That is,        there a method to reliably estimate the MS speed? Can the        received beacon powers be measured often enough to be able to        use fast fading based methods? What signalling does the MS use        to indicate its' speed if the estimation is in the mobile?

After the MS has been commanded by the network to start theinter-frequency measurements the MS is to perform the measurements onthe frequency given in the start measurement command.

The algorithm is used to trigger the transmission of the inter-frequencymeasurement report. In the algorithm the UL and DL directions oftransmission are treated separately. So, actually two decisionalgorithms, DLU and ULU function in the MS independently. The outputs ofthese algorithms are combined as shown in FIG. 3 to make the finaldecision concerning sending the measurement report. The network cancommand the MS to use either one of them or both for the triggering ofmeasurement report transmission. It should however be noted, that theactive set is always the same for both directions of transfer.

The algorithm includes the below threshold. For the threshold anabsolute and a relative threshold CF_abs_(th) and CF_rel_(th) aredefined. The decision flow chart for DLU unit of the algorithm is shownin FIG. 7.

If new measurement results have been acquired in the new frequency notbelonging to the active set, the link losses the beacon signal issuffering are compared to an absolute threshold CF_abs_(th). If thequality of the link is sufficient it is compared to the best link in theactive set. If the quality is better with a predetermined margin theoutput of the DLU algorithm is set to TRUE.

A similar algorithm ULU is run for downlink direction. The outputs ofDLU and ULU are combined using a logical function as described earlier.

When the HO algorithms trigger the inter-frequency measurement reportthe status of the M best cells/sectors is transmitted. The M bestcells/sectors are determined by using the values of S_(i,dl) or S_(i,ul)depending on whether it was DL or UL algorithm that triggered thereport. The contents of the report is determined with a message sentfrom the network. The measurement report includes, e.g. the followingvalues for each cell/sector to be reported. These values are thefiltered values.

-   -   1. S_(i,dl)    -   2. S_(i,ul)    -   3. L_(i)

It must be noted that the possible logical functions are not limited tothose presented in the examples above. For instance, if the outputs ofthe DLU and ULU functions are not binary but have more levels or areeven continuous functions triggered by some events on the radio signalsin respective directions, fuzzy logical functions can be used whenmaking the decision whether to send or not to send a measurement reportbased on the outputs of the functions DLU and ULU. The fuzzy logicalfunctions are preferably given by the network.

Periodic Handover Reporting

In a periodic measurement scheme the MS continuously performsmeasurements on the radio signals. The measurement report is to betransmitted periodically by the MS to the network. The transmissionperiod is defined by the parameter T_report set by the network. It shallinclude the M best cells/sectors. The transmitted measurement report isalways to include also the appropriate values for the active set.Whether the order of the sectors is set by S_(i,dl) or S_(i,ul) is setby the network.

The measurement report includes, e.g. the following filtered values foreach cell/sector to be reported. These values are the filtered values.

-   -   1. S_(i,dl)    -   2. S_(i,ul)    -   3. L_(i)

It should be noted that the measurement report can include informationonly about neighbour BTSs whose beacon signals have been decoded. Thusthe handover report has to include the information of the number of BTSsthat are being reported. The parameters defined by the network arepreferably similar to those defined in the MEHO case presented above.

Condition Change Based HO Reporting Scheme

The transmission of a condition change based measurement report istriggered if the conditions change by a sufficient amount. The amount ofchange needed is set by the network and denoted as Change_(th) (dB).

In this reporting scheme, the MS keeps a list of the N (a parameterpreferably defined by the network) best BTSs. The order is determined byusing either S_(i,ul) or S_(i,dl) (preferably an option set by network).When the value of S_(i,ul) or S_(i,dl) for one of these BTSs changes byChange_(th) a measurement report for including the new values of thechanged quantities is transmitted. A measurement report is alsotransmitted if a new BTS appears, that is better than Replace_(th) (dB)compared to the worst BTS (the value of S_(i,ul) or S_(i,dl) is used forthis comparison depending on how the BTSs are placed in order) in thelist. A measurement report can be at most transmitted every T ms (thisis a network parameter).

This method requires, that the MS keeps in memory in a table the valuesof the parameters transmitted in the previous measurement reports. Thatis, the MS has to keep in memory the situation as the network sees itbased on the measurement reports transmitted by the MS. This table mustinclude as its' elements the values of the quantities required (by thenetwork) to be reported and the set of reported base stations, i.e.those base stations whose beacon signal measurements are reported. Theformat of this table, i.e. the HO_table is thus for example thefollowing: S_(i, dl) S_(i. ul) L_(i) P_beacon_(tx. i) BTS₁ . . . BTS_(n)

An implementation for the decision diagram for sending a conditionchange based measurement report is depicted in FIG. 8. Having measuredthe signals (stage C1) and sent a measurement report (stage C2), theprocedure waits for a delay T defined by the network (stage C3). Atstage C4 the best signal of those beacon signals that do not belong tothe set of reported base stations, i.e. the candidate base stations, iscompared to the worst signal of those beacon signals that belong to theset of reported base stations. If the signal quality of the candidatebase station exceeds that of the worst reported base station by a marginreplace-th defined by the network, the worst base station is replaced bythe candidate base station in the set of reported base stations (stageC10). The HO-table is updated (stage C11) and a measurement reporttransmitted (stage C12).

If there is no need to update the list of reported base stations, thechanges in the measured signal values are compared to the giventhresholds at stage C5. If the thresholds are not exceeded, theprocedure returns to stage C4. If at least one of the thresholds isexceeded, a measurement report is generated (stage C11) and transmitted(stage C12).

The contents of the measurement report may be the same as the elementsin HO_table for the BTSs whose measurement value (S_(i,ul) or S_(i,dl))have changed. The measurement report/HO table can include, for example,the following filtered values for each cell/sector to be reported:

-   -   1. S_(i,dl)    -   2. S_(i,ul)    -   3. L_(i)

The inter-frequency scheme for the condition change based reportingscheme is the same as the intra-frequency scheme except that the networkcommands the MS to initiate the measurements only when needed.

A network functionality's according to the invention are shown in FIG.9. The network comprises

-   -   determining means for determining a plurality of independent        trigger conditions    -   sending means responsive to the determining means for sending        the determined trigger conditions to a mobile station.

The sending means may send the threshold values to the correspondingmobile station using the Dedicated Control Channel DCCH associated witha traffic connection to the mobile station, for example. These means arepreferably implemented in a single network element of the network, suchas in the Radio Network Controller RNC.

In one preferred embodiment, one of the determining means determinesthresholds for triggering the sending of a measurement report in themobile station when at least one upper threshold for a mobile evaluatedhandover is exceeded or lower threshold gone under. An example ofsuitable parameters for such thresholds was given above.

In one preferred embodiment, one of the determining means determinestrigger conditions for the transmission of a measurement report in themobile station periodically. In this case, the determining meansdetermine the suitable period for measurement reporting.

The determining means are preferably arranged to define the activity ofrespective trigger conditions, and the sending means are arranged tosend this information to the mobile station.

According to yet another embodiment, one of the determining meansdetermines thresholds for triggering the sending of a measurement reportin the mobile station triggered by a change in the radio resourcesexceeding a threshold given by the network. An example of suitableparameters for such thresholds was given above.

A mobile station MS according to present invention is shown in FIG. 10.The mobile station comprises

-   -   receiving means for receiving from the network trigger        conditions for the transmission of a measurement report,    -   monitoring means for monitoring the radio signals,    -   a plurality verifying means which is responsive to the receiving        means and the monitoring means and which has the functionality        of verifying whether the trigger conditions for sending a        measurement report of a specified type are met,    -   a plurality of report means responsive to the verifying means        for establishing a measurement report, and    -   sending means responsive to the report means for sending a        measurement report to the network.

Preferably, the mobile station further has

-   -   determining means (DLU, ULU) for verifying trigger conditions        for uplink and downlink measurements separately to generate two        different verification results and    -   combining means responsive to the determining means for        combining the verification results and to make the decision        whether to send or not to send a measurement value,

as shown in FIG. 3.

The measurement reporting scheme according the invention providesflexible means for reporting measurement results. The advantage of theflexibility is that the measurement reporting can be adjusted to providethe network the necessary information while minimizing the amount ofradio resources spent for the measurement reporting purposes.

The invention has been described above by means of preferred embodimentsto illustrate the principles of the invention. As regards the details,the invention may vary within the scope of the attached claims. Forexample, the trigger condition for sending a measurement report may be athreshold for a linear combination of the downlink and uplinkmeasurement results. In this case, the function defining the linearcombination is preferably defined by the network.

1-30. (canceled)
 31. A method of measurement reporting in atelecommunication system comprising mobile stations and a networkcomprising base stations, wherein decisions upon establishing orcanceling a link between a mobile station and a base station are made inthe network on the basis of measurement reports sent from the mobilestation to the network, wherein the method comprises the steps ofdefining for a mobile station at least one active measurement reporttrigger from a group of measurement report triggers, monitoring at themobile station properties of a plurality of radio signals received fromrespective base stations, and generating at the mobile station ameasurement report comprising information about the monitored radiosignals when at least one active trigger is met.
 32. A method accordingto claim 31, wherein the active triggers are defined by the network. 33.A method according to claim 31, wherein the method further comprises astep of resetting a timer in connection with the step of transmitting ameasurement report, and at least one active trigger comprises acondition for the value of the timer.
 34. A method according to claim31, wherein at least one of the triggers is a threshold for a radiosignal parameter or a function thereof.
 35. A method according to claim34, wherein the radio signal parameter is the received power level ofthe signal or a function thereof.
 36. A method according to claim 34,wherein the radio signal parameter is the interference in the receivedradio signal or a function thereof.
 37. A method according to claim 36,wherein the network uses CDMA air interface in which the connections areseparated using different spreading codes, and the value for theinterference is an estimate for the interference power made before orafter the signal is correlated with the spreading code used in theconnection.
 38. A method according to claim 31, further comprisingdynamically defining for a mobile station at least one activemeasurement report trigger from a group of measurement report triggers.39. A method according to claim 34, wherein at least one active triggercomprises a base station specific offset value.
 40. A method accordingto claim 39, wherein the network dynamically defines the offset values.41. A method according to claim 34, wherein one active trigger comprisesa threshold for the change of a radio parameter or a function thereof.42. A method according to claim 34, wherein a first set of triggers isdefined for the radio signals in the uplink direction and a second setof triggers is defined for the radio signals in the downlink direction,a logical function is defined for combining the first and the second setof triggers, and at the mobile station, the state of each trigger isdetermined, the states combined using the logical function, and themeasurement report is sent in dependence upon the condition of thelogical function.
 43. A method according to claim 42, wherein the firstand second set of triggers are dynamically defined by the network.
 44. Amethod according to claim 42, wherein the logical function is defined bythe network.
 45. A method according to claim 42, wherein a firstcombination of the first and second sets of triggers and the logicalfunctions are defined to be used for radio signals from or to activebase stations having an active link with the mobile station, a secondcombination of the first and second sets of triggers and the logicalfunctions are defined to be used for radio signals from or to candidatebase stations not having an active link with the mobile station, and atthe mobile station, the first combination is used for radio signals fromor to active base stations and the second combination is used for radiosignals from or to candidate base stations.
 46. A method according toclaim 45, further comprising the step of creating an active link betweenthe mobile station and a candidate base station not having an activelink with the mobile station when the network receives from the mobilestation a measurement report triggered by that candidate base station.47. A method according to claim 45, further comprising the step ofdeleting an active link between the mobile station and a base stationwhen the network receives from the mobile station a measurement reporttriggered by that active base station.
 48. A method according to claim45, wherein said two different logical functions are such that when abase station is in the active set, a measurement report is not triggeredby a radio signal of that base station for the same set of radioproperties as would trigger the transmission of a measurement reportwhen the base station is in the candidate set.
 49. A method according toclaim 42, wherein the method comprises a step of defining a logicalfunction for use when the number of base stations in the active set isequal to a predefined maximum number, and defining the first and secondsets of triggers on the basis of the radio signal properties of theactive base station having the worst signal conditions, and wherein ameasurement report is triggered by a radio signal of a candidate basestation causes that worst base station to be replaced by the candidatebase station.
 50. A method according to claim 49, wherein the maximumnumber is dynamically defined by the network.
 51. A method according toclaim 31, wherein the network informs the mobile station whatinformation to include in the measurement report, and the mobile stationincludes this information in the measurement report.
 52. A methodaccording to claim 51, wherein the radio signals are ordered using apredefined condition, and in the measurement report sent from the mobilestation, information about the properties of a predefined number of thebest radio signals according to the condition are reported.
 53. A methodaccording to claim 51, wherein the number of radio signals to bereported is given by the network.
 54. A method according to claim 51,wherein the measurement report comprises a value for the path loss for areported signal or a function thereof.
 55. A method according to claim51, wherein the measurement report comprises a value for the carrier tointerference ratio of a reported signal or a function thereof.
 56. Atelecommunication network for a telecommunication system comprisingmobile stations and a network comprising base stations, in which systemthe mobile stations are adapted to monitor radio signals sent by thebase stations, wherein the network comprises means for determining for amobile station at least one active measurement report trigger from agroup of measurement report triggers for triggering the transmission ofa measurement report from the mobile station, and means forcommunicating the determined at least one active trigger to the mobilestation.
 57. A telecommunications network according to claim 56, whereinthe network is arranged to repeatedly determine the activity of the atleast one measurement report trigger.
 58. A network element for atelecommunication network for a telecommunication system comprisingmobile stations and a network comprising base stations, in which systemthe mobile stations are adapted to monitor the radio signals sent bybase stations, wherein the network element comprises means fordetermining for a mobile station at least one active measurement reporttrigger for triggering the transmission of a measurement report from themobile station, and means for communicating the determined activetriggers to the mobile station.
 59. A mobile station for atelecommunication system comprising mobile stations and a networkcomprising base stations, in which system the mobile stations areadapted to monitor radio signals sent by the base stations, wherein themobile station has means for receiving from the network a determinationof at least one active trigger from a group of measurement reporttriggers for triggering the transmission of a measurement report, meansfor monitoring the properties of a plurality of radio signals receivedfrom respective base stations, means for verifying whether an activetrigger has been met, means for generating a measurement reportcomprising information about the monitored radio signals responsive toverifying that at least one active trigger is met.
 60. A mobile stationaccording to claim 59, comprising means for receiving at least first andsecond different set of active triggers for uplink and downlink signalsrespectively, and a determination of a logical function for combiningthese sets of triggers, means for determining the state of each activetrigger and to combine the states according to the logical function, andthe means for generating the measurement report is configured toestablish a measurement report in dependence upon the condition of thelogical function.
 61. A decision unit for a mobile station in atelecommunication system comprising mobile stations and a networkcomprising base stations, wherein the mobile stations are adapted tomonitor radio signals sent by the base stations, wherein the decisionunit has means for receiving from the network a determination of atleast one active trigger from a group of measurement report triggers fortriggering the transmission of a measurement report, means formonitoring the properties of a plurality of radio signals received fromrespective base stations, means for verifying whether an active triggerhas been met, and means for invoking generating a measurement reportcomprising information about the monitored radio signals responsive toverifying that at least one active trigger is met.